Clinton's campaign flubbed another angle of this scandal too. Trump defended himself by saying "All men talk like this." If Hillary had gone after that statement by saying that most men don't talk or act like that, and that Trump is a malignant anomaly, she'd have positioned herself as defending men against Trump's obvious, slanderous lies.
Or it could open up another can of worms and make her appear more moralizing.
Really, a "Patriots over Prostitutes" sort of approach would've been a much better angle.